Field of the Invention
The present invention relates to an excitation device of an AC exciter which is used for start-up of a power generating device that is configured by a gas turbine and a power generator.
Background Art
In recent years, power generation facilities with high efficiency have been required from the viewpoint of the environment, and for this reason, combined cycle power generation which uses a gas turbine (GT) has increased. On the basis of this, the capacity of the gas turbine has been increased.
In the gas turbine, combustion air is compressed by a rotary compressor and the compressed combustion air is transferred to a combustor, fuel is absorbed into the combustor to be burned, and the combustion gas with a high temperature and a high pressure which occurs at that time rotates the turbine. A turbine shaft is directly coupled to the compressor, and compression power is transferred to the compressor thereby continuously driving the compressor. For this reason, at the time of start-up of the gas turbine, it is necessary to drive the compressor and a power generator which have great resistance torque using a start-up motor or the like until the gas turbine is ignited and reaches a rotation speed by which self-drive can be performed.
In this situation, a method of starting up the gas turbine is increasingly used which does not require a start-up motor and a torque converter whose sizes increase in accordance with a large capacity of power generation facilities, has no voltage drop of a house power supply due to a start-up current of the motor, uses a speed-variable inverter that can shorten axial length, and uses the power generator as a synchronous motor by converting the frequency of a commercial power supply.
At this time, it is necessary to transfer an excitation current of approximately several hundred amperes from a turning rotation speed (several times/min) to a rated rotation speed, to a field magnet winding wire of the start-up motor. However, in a normal AC exciter method, and particularly in a brushless excitation method, an AC generation voltage of the AC exciter is low and thereby sufficient excitation cannot be made in an area in which rotation speed is low such as several times/min. For this reason, thyristor excitation which can excite a field magnet winding wire by using a slip ring regardless of rotation speed is generally used.
An AC exciter which is used for a brushless excitation method generates magnetic flux using a current flowing through the field magnet winding wire, and as an armature winding wire of the AC exciter which is directly coupled to the field magnet winding wire of the power generator through a rotation shaft is interlinked with the magnetic flux, excitation power necessary for power generation is generated. If the AC exciter is a synchronous apparatus, a voltage which is applied to the field magnet winding wire is generally a DC voltage, but a three-phase winding type induction apparatus is used as the AC exciter, and as a field magnet winding wire on a primary side is set as a three-phase winding wire and an AC voltage is applied, an AC voltage is generated on a secondary side. By the excitation, start-up of a speed-variable inverter device, which is not possible in a brushless excitation method of the related art, can be made (for example, JP-A-2003-143899).
FIG. 21 is a circuit configuration diagram of a turbine power generator with a brushless exciter of the related art which can start up a gas turbine power generation device by using a speed-variable inverter device, by using a three-phase induction apparatus as an AC exciter. At the time of start-up, a three-phase AC voltage which is generated in an armature winding wire 11 is rectified by a diode of a rotation rectifier 12 and thereby becomes a DC voltage. A DC terminal of the rotation rectifier 12 is coupled to a field magnet winding wire 21 of a main power generator 2 within a rotator 4, and the field magnet winding wire 21 of the main power generator 2 becomes the rotator 4 having a magnetic polarity in a constant direction. For this reason, a variable speed inverter device 23 for start-up is coupled to an armature winding wire 22 of the main power generator 2, speed-variable power is generated by using a house power supply 71 as an input, and if a rotation magnetic field is generated in the armature winding wire 22 of the main power generator 2 and is gradually increased from a low frequency, the main power generator can be started up as a synchronous apparatus without providing another particular motor for acceleration.
In addition, after start-up and at the time of a normal drive, an excitation rectifier 43 uses an AC voltage of a permanent magnet power generator (PMG) 40 as a power supply, and rectifies an AC voltage to a DC voltage using a thyristor rectifier. As a DC excitation of a field magnet winding wire 18 of an AC exciter 9 is performed, a three-phase AC voltage is generated in the armature winding wire 11, the three-phase AC voltage is converted into a DC voltage by the rotation rectifier 12 in the same manner as at the time of start-up, a current flows through the field magnet winding wire 21 of the main power generator 2, a voltage is generated in the armature winding wire 22 of the main power generator 2, and thereafter, the voltage is synchronously input to a system power supply 72.
However, the excitation device of the AC exciter of the related art needs to establish excitation of the field magnet winding wire of the main power generator, at the time of start-up which is performed by the speed-variable inverter device. Thus, at the time of start-up, AC excitation of the field magnet winding wire of the AC exciter which employs the three-phase induction apparatus is performed, and thereafter, a gas turbine drives itself and thereby it is necessary to perform DC excitation at a point of time when the gas turbine reaches a rotation speed close to the rating. For this reason, there are problems in which a three-phase current adjustment apparatus and a thyristor for start-up, and an excitation rectifier that is used after the start-up are required as the excitation device of the AC exciter, and in addition, with respect to the field magnet winding wire of the AC exciter, a contactor for AC excitation and a contactor for switching to a rectifier for DC excitation are essential, and an output circuit is complicatedly configured.